Load maneuvering apparatus



June 15, 1965 w. c. CARL ETAL LOAD MANEUVERING APPARATUS Filed Jan. 25, 1963 ml-I..

NEM.

d sm R O u MU T. g N NHn R EU O VC| T N 0 T. if nnvA r .m0 HW e0 WH WITNESSES United States Patent O 3,189,i% LAD MANEUVERNG APPARATUS Weliington C. Carl, Chnrchiii, and Howard A. Zoliinger,

Monroeville, Pm, assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed dan. i963, Ser. No. 253,369 '7 Claims. (Si. 'Zlib-llt) This invention relates to apparatu-s for maneuvering, i.e., holding, positioning or moving, a load between two stations which are subject to relative movement between each other. rfhis invention is particularly useful in maintaining a constant position or constant velocily of a load being held or transferred between a fioating vessel and another station such as a dock, another floating vessel, an underwater structure, the bottom of the sea, or any other selected reference point.

When a load is being lifted from a ships deck by a crane located on the doch, if the crane operator misjudges the ships position due to wave movement and hoist s eed, the ship may rise on the wave and hit the load before it is clear. On the other hand, when a load is being placed on the ship the operator must try to judge the roll and pitch of the ship, or the load may hit the deck too hard. In either case damage to both the load and ship is possible.

`For convenience, the station on which the load moving apparatus such as a crane is located, will be referred to as the active station, while the other station will be referred to as the passive station. In the ship and dock example, the dock is the active station if the crane is on the dock. The ship in that case is the passive station.

One aspect of the present invention contemplates apparatus for controlling the movement of a load between two stations to control the load to desired constant velocity relative to the passive station while the stations are subject to relative movement between each other. This may include the case where the desired constant velocity is zero, in which case the position of the load is held constant relative lto the passive station. This is accomplished in accordance with one embodiment of the invention by a hoist controlled by resultant forces produced from a desired speed command signal, an actual load speed signal, and a signal which is a function of the relative motion between the stations. More specifically, in accordance with one embodiment, the speed regulated hoist is made responsive to a signal which is a function of the relative motion between said stations thereby to compensate for such relative motion. i

it is therefore an object of the present invention to provide apparatus for compensating for the relative motion between two stations between which a load is being maneuvered.

Another object ofthe invention is to provide apparatus for maneuvering a load between active and passive stations at a constant desired velocity relative to the passive station, while there is relative movement between the stations.

Another object is directed to reducing or eliminating the effect of relative motion between active and passive stations on the velocity or position of a load relative to the passive station.

Other objects and advantages of the present invention will become apparent from the following description taken in connection with the accompanying drawing, wherein there is illustrated a preferred form of the invention as embodied in a hoist system for transferring loads between a dock and a floating vessel. ln order to Simplify the illustration of the invention, auxiliary equipment, such as breakers, relays, electrical interlocks, brakes, etc., usually found in apparatus of the character described, is not shown.

in the drawing, there is sho-wn a diagrammatic representation of a crane iii mounted on a dock l2 for transferring a load ld between the dock and a floating vessel lo?. around a sheave 2i) on the outer end of a boom 22, and reeled on a drum 2d driven by a reversible drive 26. The drive 26 includes a motor 2@ mounted on the crane and a control system 3h for controlling the speed and direction of the motor, and thereby of the load, by controlling the electric power supplied from a suitable source to the motor. By way of example, the motor 28 is shown as a three-phase squirrel cage motor supplied from supply lines Ll, L2 an L3 connected to a source of three-phase power (not shown).

The control system Bil includes a variable impedance arrangement 3ft interposed in the motor 2S supply lines, and controlled in response to a desired load speed reference or command signal A, an actual load speed signal B, and a signal C representing the relative motion between the ship and the dock. These signals are applied to a summing circuit 36 which controls the variable impedance arrangement 34 to provide speed and reversing control.

More specifically, power line Ll is connected through the main winding 33 of a saturable reactor 49 to a terminal Ti of the motor 2S. Line Ll is also connected through the main winding il of a saturable reactor 42 to a terminal T3 of motor 2S. In like manner line L3 is connected to terminals Ti and T3 through the main Windings 45 and 47 of saturable reactors d4 and 46 respectively. For convenience, reactor it? and to will be referred to as the hoist reactors While reactors ft2 and 44 will be referred to as the lowering reactors. Line L2 is connected directly to terminal T2 of the motor.

Control windings 4S and Sti of the hoist reactors 4i) and 46 are connected together to the D.C. output S2 of a magnetic amplifier 62 which mayfconveniently be referred to as the hoist pilot amplifier. Likewise, control windings 64 and 66 of the lowering reactors 42 and i4 are connected together to the DC. output 67 of a magnetic amplifier 63 which may conveniently be re ferred to as the lowering pilot amplifier. It should be apparent that the hoist reactors are driven in unison in the same direction by the hoist amplifier 62, either up or down, and that the lowering reactors are driven together in the same direction either up or down by the lowering amplifier 68.

Amplifiers 62 and o8 are provided with control Windings 79 and 72 respectively connected in series opposition so that a common signal flowing through the conrol windings affects the amplifiers in opposite sense. More specifically, a common control signal through the control windings 76* and 72 will tend to drive the amplifiers 62 and 68 in opposite directions, that is drive one up while the other is driven down. A bias circuit 74 is arranged to bias the hoist and the lowering amplifiers to cuto at quiescent. Thus with no signal in the control windings 79 and 72 the respective amplifiers 62 and 68 do not produce an output and the hoist and lowering reactors will be unsaturated, each presenting maximum impedance in its line.

The polarity dot convention employed in the drawing in connection with the hoist and lowering amplifiers signies that a current of positive polarity applied at the dotted end of a winding will tend to drive the amplifier up, the converse being true when a signal of negative polarity is applied to the dotted end of a Winding.

From the foregoing it should be apparent that a net positive signal on a line 76 connected to the control windings 70 and 72 will drive the output of the hoist amplifier 62 upward and tend to drive the output of the lowering The crane includes a load lifting cable 1S reeved annales rg n; amplier 68v down. This saturates the hoisting reactors 4t) and 46, while the lowering lreactors 42 and 44 remain unsaturated. Thus the impedance of reactors 4@ and 46 are reduced, thereby effectively connecting line Ll. to terminal Tll and line L3 to terminal T3, thus providing a particular phase rotation to drive the hoist motor 28 in the hoist direction. In the meantime reactors 42 and 44 remain at their maximum impedance, and as a result the circuits from L1 to terminal T3 and from L3 to terminal T1 are substantially open circuits.

On the other hand, if a negative signal is applied to the line 76 the lowering amplier 68 is driven up while the hoist amplifier 62 is held to no output. These conditions saturate the lowering reactors 42 and 44 while the hoist reactors 4t) and 46 remain unsaturated, and as a result line L1 is eiectively connected to terminal T3 of the hoist motor 2S and line L3 is effectively connected to terminal Tl of the motor thereby producing a reversed phase rotation to drive the hoist motor in the lowering direction.

In addition, the saturation of the hoist vand lowering reactors may be controlled between zero and maximum, thereby controlling the motor torque or speed in the chosen direction by varying its primary voltage.

Control windings "itl and 72 of the hoist and lowering amplifiers are connected' in the summingcircuit 36 in series opposition as hereinbefore mentioned whereby the net signals developed by the summing circuit 36 are supplied in push pull to the control windings of the hoist and lowering ampliliers 62 and 68.

Connected into the summing circuit 36 is a desired speed reference signal source 80 for supplying to the summing circuit a desired speed reference or command signal A representing a desired direction and speed of the load 14. In the source 80 there is a split potentiometer S2 connected across a D.C. source, for example the battery shown at 84. A iixed center tap 86 on the potentiometer is connected to a conductor 87 of the mixing circuit 36. The potentiometer 82 is provided with a movable tap 88v mechanically linked to a master controller handle 90 and electrically connected through conductor 76 to the dot end of control winding 70 of the hoist ampliier 62. The controller handle 90 also operates a drum switch 91 in unison with the pot arm 8S.

When the potentiometer arm 88 is moved to the hoist side by the control handle 90, a positive voltage is applied to line 76. On the other hand, when the arm 88 is moved to the lowering side, a negative voltage is applied to line 76. The magnitude of the output voltage of source 80, adjustable by means of handle 90, is selected to correspond with the desired speed of the motor and load movement. Thus the speed of load movement will be dependent on the magnitude of the voltage supplied by source 80, which in turn is dependent on the position of the potentiometer arm 63 as determined by the handle 90.

A signal B representing the actual speed of the load 14 relative to the crane 10 is injected into the summing circuit 36 by a D.C. tachometer 94, which is mechanically coupled to the output shaft 95 of the hoist motor 23. VThis tachometer provides an output Voltage with a magnitude proportional to the motor speed and a polarity dependent on the direction of motor rotation.

In theparticular arrangement shown, and as indicated by the legends under the tachometer, the tachometer 94 generates a positive voltage at its output terminal 96 when the hoist motor 28 is hoisting, and a negative voltage at terminal 96 when the hoist motor 28 is lowering. One output terminal 96 of tachometer 94 is connected through a current limiting resistor 9S to the dot end of the control winding 72 of the lower pilot amplifier 68. The other output terminal 100 of this tachometer is connected through a resistor 102 to the line 87.

At 104 there is shown a ships motion reference circuit which, when connected into the summing circuit 36 by a switch 106, supplies to the summing circuit a signal C which is proportional to the velocity of the relative vertical movement between the ship 16 and the crane 22. Included in the circuit 104 is a DC. tachometer ltll mechanically driven by a sheave lll) rotatably mounted on the crane boom 22. The pulley 110 is rotated by the vertical motion of the vessel 16 in one or the other direction by means of a tag line 112 reeved around the pulley Il@ and secured at one end 114 to the ship 16, while the free end of the line is weighted at 116 to maintain constant tension on the line. A suitable guide pulley may be employed to keep the weighted side of the line free from entanglement. Such a guide pulley may be fastened on the crane boom 22 or the dock l2, as shown.

One output terminal T20 of the ship motion tachometer 103 is connected to one side of switch T06, the other side of the switch being connected to a junction 122 between one end of resistor MBZ and the output terminal lil() of the load velocity tachometer 94. yThe other output terminal 124 of the ships motion tachometer 108 is connected through a one way valve 126 to the other end of resistor 102. Means for shunting the one way valve 126 during the lowering operation is provided by a switch segment 134i of the drum switch 91 which segment shorts a set of contacts 132 when the controller handle 9@ is moved to the lowering position. Contacts 132 are connected on opposite sides of the one way valve 126. Thus, when switch 196 is closed the tachometer lltl is connected across the resistor N2 either through the one way valve 3126 or through the shorted contacts 132 around the valve, as the case may be. In either event, a signal C representing and responsive to relative vertical motion between the vessel I6 and the crane boom 22 is injectedV Operation without the slzips motion reference The system illustrated `with only the command signal source 30 and the l-oad speed reference source 94 connected into the summing circuit 36, but without the ships motion reference circuit rtl4, constitutes a well known speed regulated hoist system, Le., the load speed for any given command or reference speed is maintained oonstant relative to the crane and dock l2. The operation of this prior art portion of the system will now befbrietiy described.

As hereinbefore stated the command or desired speed reference signal A from the command source Sil, for any given command direction is opposed in the summing circuit 36 by theA actual motor speed signal B produced by K tachometer 94. The differentially combined signals A and B .are applied to the control windings of the hoist and lower amplifiers, whereby these amplifiers respond to the dierential between signals A and B, which is the regulating error in the system. The magnitude and polarity of the command signal A from the command source is dependent on the desired speed and direction of the command. The magnitude and polarity of the output of tachometer 94 is dependent on the speed and direction of rotation of the hoist motor 28. Thus, the command signal A is proportional to desired speed, while the actual speed signal from tachometer 94 is proportional to the speed of the hoist motor.

To raise the load 14, the master control handle is moved into the hoist sector of the controller range to a selected position corresponding to the desired speed, for example, to the second hoist position. Movement of the 'enseres handle 90 into the hoist sector (leftward) moves the drum switch 91 and the potentiometer arm S3 in unison to the left or the hoist sector ofthe controller. In this sector, potentiometer arm 5t; taps into the positive side of hoist sector of the potentiometer S2 to provide a positive command signal A to the dot end of control winding 7i?, the magnitude of the signal corresponding to the selected command speed. This drives the output of the hoist amplifier 62 up to saturate the hoist reactors d@ and d6. Since a sign-al of this polarity tends to drive the lowering ampliiier 68 down, this amplifier isv held at cutoff and the lowering reactors 46 and Sti remain unsaturated and at maximum impedance. The hoist reactors 4t) and de are saturated to a degree dependent on the magnitude of the command signal A. As a result, motor 2S is excited in the proper phase sequence to rotate in the hoist direction. As the speed of the hoist motor increases, the output voltage of the tachometer 94, which is opposed to the command signal, increases until equilibrium is reached wherein enough excitation is supplied to the motor to produce the requisite torque to maintain the selected command speed.

It for any reason the motor 28 should run faster than the command speed, the tachometer 94 voltage will be greater than the command signal A and the polarity of the resulting error signal will be such as to apply positive voltage to the dot end of control winding '72 and nega tive voltage to the dot end of control winding 79. The net result of this is a reversal of the phase sequence applied to the motor and .a consequent application of countertorque within the motor or plugging thus, slowing the motor down until equilibrium is reached at the proper speed and torque.

To lower the load, the command signal A is reversed in polarity by moving the master control handle 9d to the lowering sector, thus moving the potentiometer arm 8S to that side of the potentiometer which will produce a positive signal at the dot end of control winding 72 and a negative signal at the dot end of control winding 7d, thereby driving the output of the lowering amplitier 68 upward to produce the proper phase sequence at the motor 28 terminals to rotate the m-otor in the lowering direction.

In the lowering direction tachometer 9d produces an output voltage which is positive at terminal Id@ thereby opposing the command signal A which for the lowering direction is negative at the potentiometer arm 83 and positive at the tap 36. At the speed of the load increases in the lowering direction, the tachometer 94 output voltage increases. If in lowering, the load tends to overhaul the motor, the tachometer 9d voltage will exceed the command signal A thereby saturating the hoist reactors to provide suiiicicnt countertorque to keep the load at the command speed.

In summary, the system whose operation has just been described is known as a speed regulated system wherein the speed of the hoist motor is regulated or maintained constant tor any given command signal. In this system the load movement is maintained at a constant speed relative to the crane 22 and dock 12 for a given command speed. It can also be seen toom the above operational description that, although the load speed is constant relative to the crane and crane support, the speed of the load relative to the ship is undesirably variable due to `the rise and fall of the ship because of wave action. The present invention as will now be more specifically described is directed to a reduction or elimination of the variation in speed of theload relative to the ship due to the relative vertical motion between the ship and the crane.

Operation with the shz'ps motion signal To minimize the effect of the ships motion in accordance with one embodiment of the'invention, the ship mod tion reference circuit 104 is added to the summing circuit 36 by closing switch 106.

In hoisting a load, the direction of relative movement between load and ship is away from each other, that is, in the Opening direction. Likewise, when wave motion causes the ship to fall away from the load, the relative motion between the ship and the crane and also between the ship and the load is in the Opening direction. On the other hand, when the loadis being lowered to the ship, the direction of relative movement between ship and load is in the Closing direction. Likewise, if wave motion causes the ship to rise toward the load, the direction of relative movement between the ship and the crane and between the ship and the load is in the Closing direction.

When it is desired to compensate for the relative motion between the ship and the crane, the switch ldd is closed. The polarity relation of the ship motion reference circuit 104 to the rest of the summing circuit 36 is such that the command signal A from the desired speed reterence source 8d and the ship motion signal C from the ships motion reference source lddare in mutually aiding relation when the direction ot relative movement between the ship and the crane is opposite to the commanded direction of relative movement between the load and the ship. In other words, for this circumstance the signals A and C have similarly sensed control effect on the control system 3d. On the other hand, signals A and C are in mutually opposing relation providing oppositely sensed con-trol effects on the control system 3d when the relative movement between the ship and the crane is in the same direction as the commanded relative movement between the load and the ship.

As hereinbefore stated, when the ship is rising, that is, when the direction of the relative movement between the ship and the cra-ne is in the Closing direction, the ships motion tachometer 1% provides a negative output at its terminal 120, the terminal 124 then being positive. However, When the ship is falling, that is, when the relative movement between the ship and the crane is in the Opening direction, the output of the ship motion tachometer 108 is positive at terminal 120 and negative at terminal 124.

From the above, it should be apparent that the ship motion signal C from the tachometer 1% aids the command signal A from the source Sti when the relative movement between the ship and the crane is in the direction tending to oppose the purpose of the command ysignal A, and signal C opposes signal A when the direction of relative movement between the ship and the crane aids the purpose of the command signal A. It should be apparent that a falling ship opposes the purpose of a Ilowering command, while a rising ship aids the purpose of a lowering command. Also, n hoist command is opposed by a rising ship, and aided by a falling ship.

These relations reverse when the position of the crane is reversed, that is when the crane is on the ship. In the latter case a falling ship aids the purpose of a lowering command, while a rising ship opposes the purpose of a lowering command. Also with the crane on the ship, a hoist command is aided by a rising ship, and opposed by a falling ship.

The operation will now be considered in more specific detail. Suppose that a load is to be transferred from the dock to the ship. With the switch 106 open, the crane operator swings the crane 22 around its Vertical pivot to a position over the load on the dock. The load is hooked to the line 18 and the crane operator raises the load by operating the master control 96 to the hoist side, the load is then held in a hoisted position by just enough hoist command signal A to provide stall torque, and the crane is swung around its vertical pivot to position the load over the ship. The crane operator then closes switch ltle. The drive system now will `follow the ships motion signal and tend to maintain a constant distance between the load and the ship.

atentos a' in order to lower the load to the shipsdeck the crane operator moves the master control 90 to the lowering side to provide a lowering command signal which is negative at the dot end of the control winding 70; In this position of control 90, contacts 132 are bridged by switch;

segment 130 to shunt the one Way valve 126. As the load starts to move down, the speed feedback tachometer 94 puts out a negative signal at its terminal 96 which opposes the command signal. If in the meantime the ship is rising, the ship movement tachometer 108 generates a negative signal at its terminal 120 which opposes the command signal and forces the drive to run slower. if, as the ship is rising, the ship movement tachometer signal C exceeds the command signal A the load will actually be hoisted.` On the other hand, if, as the load is being lowered, the ship is falling, the ship movement tachometer to@ output signal C will be positive at its terminal 120 thus aiding the command signal A, thereby causing the drive to lower faster. Thus the application of the ship motion signal C to the regulating loop regulates the drive to maintain a constant speed between the load 14 and the ship 16 for any selected command speed.

When it is desired to lift a load from the ship, the crane operator moves the master controller 90 to the hoist position applying a positive signal to the dot end of control winding 7i?. As the load rises, the speed feedback tachometer 94 generates a positive signal at its terminal 96 tending to cancel the command signal to keep the drive at a -constant speed relative to the dock. If the ship rises as the load is being hoisted, the ship movement tachometer lith generates a negative signal at its terminal 120 thus aiding the command signal and forcing the drive to hoist faster, thereby to maintain constant hoisting speed between the load 14 and the ship 16;

it wil-l be noted that when the controller 90 is in the hoist position, the contacts T32 in the drum switch are open so that the ship motion tachometer 108 output is applied to the summing circuit 36 through the one way valve 126. This valve is so poled or oriented that it blocks the output of the ship motion tachometer 108 when the ship is falling, thus not slowing down the hoist as it is leaving the ship.l This is made effective only in hoisting, where it is useful, by leaving the contacts 132 open on hoisting and closing them on lowering.

As seen from the description herein, the present invention makes the motor 2.8 hoist or lower at a speed necessary to keep the load moving with respect to the ship at the speed set by the master control 90 regardless of the up and down movement of the ship.

Although above water stations have been illustrated, the invention is also very useful in the case where a hoislt on a vessel floating on the surface of the water lowers and hoists objects to and from an underwater station such as selected underwater reference level. The invention helps to avoid sudden load changes due to the friction or retarding effects of the water as the ship rises and falls with the v waves or swells.

The invention is not limited to the particular reversible drive and control therefor shown by way of example. Other suitable reversible drives and controls therefor may be employed in practicing the invention. Likewise, the ship motion signal C may be obtained by other suitable apparatus, for example, gyroscopicy systems, sonar systems, or any other apparatus which will provide a signal responsive to the relative movement between the ship and the crane. To a great extent the particular :speed of response and the degree of constancy that may be desired will govern the selection of system types, drives and control components. Thus, it isV to be understood that the herein described arrangements are simply `illustrative of the principles of the invention, and other embodiments and applications are within the spirit and scope of the invention.

the bottom of the sea, an underwater structure, or any We claim as our invention: g A

l. Hoisting apparatus for transferring a load between two stations while said stations are subject to relative vertical motion between each other, said apparatus comprising load moving means including adjustable speed reversible drive means, said drive means including a motor located on one of said stations for moving said load, control means coupled to said drive means for controlling the drive means to move said load in a direction and at a speed in accordance with signals supplied to saidcontrol means, means for providing and selectively suppl-ying to said control means either of iirst and second command signals, said first commandV signal being of one sense and a particular magnitude for commanding the control means to operate said drive means to move the load in the hoist direction at a particular speed relative to the other of said stations, said second command signal being of opposite sense and a certain magnitude for said drive means to move the load in the lowering direction at a certain speed relativeto said other station, means responsive to the relative motion between said stations for supplying a first speed signal proportional to the speed of said relative motion to said control means in said one sense when the relative motion is in a direction tending to close the gap between the load and said other station, and in said opposite sense when the relative motion is in the direction tending to widen the gap between the load and said other station, and means for providing and supplying to said control means a second speed signal representing the actual speed of said load relative to said one station and in a sense to oppose the selected one of said command signals being supplied'to said control means, said control means being operable in response to said first and 'second speed signal-s and said selected one of said command signals to operate said drive means in a manner to maintain the commanded speed and direction of movement of said load relative to` said` other station.

2. In apparatus for transferring a load between two stations which are subject to relative movement therebetween, and wherein there is a reversible drive means for moving the load, said drive means including motor means located on one of said stations for moving said load, means for providing a command signal A indicative of a desired speed and direction of movement for said load relative to the other of said stations, means forproviding a :signal B dependent on the actual speed of said load relative to said one station, means responsive to the relative motion between said stations for providing a signal C proportional to the speed of and indicative of the direc- ,tion of said relative motion between said stations, and control means coupled to said drive means and responsive to said signals A, B, and C for operating said drive means to maintain said desired speed and direction of movement of :said load relative to said other station in conformance with the ycommand of signal A, said signals A and B having opposed control effects when the load is moving in the direction dictated by the command signal A, said signals A and C being in mutually aiding relation when the relative movement between said stations is opposite to the commanded direction of relative movement between the load and said other station, said signals A and C being in mutually opposing relation when the relative movement between said stations is in the same direction as the commanded relative movement between the load and'said other station.

3. The combination as in claim 2. wherein said control means comprises summing means in which signals A, B, and C are summed to produce a resultant control effect, and means responsive to saidl resultant control effect for controlling said drive means in accordance with the command represented by signal A.

4. Apparatus for moving a load between two stations which are subject to relative movement between each other, said apparatus comprising reversible drive means for moving said load in either direction between said stations, said drive mean-s including motor means located on one of said stations for moving said load, means for providing a command signal A representing a desired speed and direction of movement for said load relative to the other of said stations, means for providing a signal B dependent on the actual speed of said motor means, tachometer generator means coupled to said stations and responsive to the relative movement therebetween for providing a signal C proportional to the speed of and indicative of the direction of relative movement between said stations, and control means coupled to said drive means and responsive to signals A, B, and C for operating said drive means to maintain said desired speed and direction of movement of said load relative to said other station in conformance with the command of signal A, `said signals A and B having opposed control effects when the load is moving in the direction dictated by the command signal A, said signals A and C being in mutually aiding relation when the relative movement between said stations is opposite to the commanded direction of relative movement between the load and said other station, said signal-s A and C being in mutually opposing relation when the relative movement between said stations is in the same direction as the commanded relative movement between the load and Vsaid other station.

5. The combination as in claim 1 and further including means responsive to the selection of said first command signal for rendering said control means unresponsive to said relative motion when said motion is in the direction tending to widen the gap between the load and said other station.

6. The combination as in claim 1 and further including a signal path along which said rst speed signal is supplied to said control means, and circuit means responsive to the selection of said first command signal for effectively connecting a one way valve in series in said path whereby said control means is rendered unresponsive to said relative motion when the motion is in the direction tending to widen the gap between the load and said other station.

7' The combination as in claim 2 wherein said apparatus is a hoisting apparatus and the relative movement between the stations is vertical.

References Cited by the Examiner UNITED STATES PATENTS 709,915 9/02 Leonard 214-13 709,916 9/ 02 Leonard 214-13 2,293,936 8/42 Crooke 212-13 X 2,702,342 2/55 Korman. 2,832,024 4/58 Wickerham 318-229 2,854,154 9/58 Hepinstall 214-14 2,946,466 7/60 Weiner 214-14 3,038,066 6/ 62 Barry. 3,088,710 5/63 Evans et al. 254-172 HUGO O. SCHULZ, Primary Examiner. GERALD M. FORLENZA, Examiner. 

1. HOISTING APPARATUS FOR TRANSFERRING A LOAD BETWEEN TWO STATIONS WHILE SAID STATIONS ARE SUBJECT TO RELATIVE VERTICAL MOTION BETWEEN EACH OTHER, SAID APPARATUS COMPRISING LOAD MOVING MEANS INCLUDING ADJUSTABLE SPEED REVERSIBLE DRIVE MEANS, SAID DRIVE MEANS INCLUDING A MOTOR LOCATED ON ONE OF SAID STATIONS FOR MOVING SAID LOAD, CONTROL MEANS COUPLED TO SAID DRIVE MEANS FOR CONTROLLING THE DRIVE MEANS TO MOVE SAID LOAD IN A DIRECTION AND AT A SPEED IN ACCORDANCE WITH SIGNALS SUPPLIED TO SAID CONTROL MEANS, MEANS FOR PROVIDING AND SELECTIVELY SUPPLYING TO SAID CONTROL MEANS EITHER OF FIRST AND SECOND COMMAND SIGNALS, SAID FIRST COMMAND SIGNAL BEING OF ONE SENSE AND A PARTICULAR MAGNITUDE FOR COMMANDING THE CONTROL MEANS TO OPERATE SAID DRIVE MEANS TO MOVE THE LOAD IN THE HOIST DIRECTION AT A PARTICULAR SPEED RELATIVE TO THE OTHER OF SAID STATIONS, SAID SECOND COMMAND SIGNAL BEING OF OPPOSITE SENSE AND A CERTAIN MAGNITUDE FOR SAID DRIVE MEANS TO MOVE THE LOAD IN THE LOWERING DIRECTION AT A CERTAIN SPEED RELATIVE TO SAID OTHER STATION, MEANS RESPONSIVE TO THE RELATIVE MOTION BETWEEN SAID STATIONS FOR SUPPLYING A FIRST SPEED SIGNAL PROPORTIONAL TO THE SPEED OF SAID RELATIVE MOTION TO SAID CONTROL MEANS IN SAID ONE SENSE WHEN THE RELATIVE MOTION IS IN A DIRECTION TENDING TO CLOSE THE GAP BETWEEN THE LOAD AND SAID OTHER STATION, AND IN SAID 